Tubing and casing (tubular goods) for oil and gas drilling and production are typically held in a storage or pipe yard after they have been received from the fabricator, or returned from a downhole installation. The storage is not permanent, but typically extends for up to a year, or until a need arises for a specific size and grade of tubing or casing. Usually, the tubular goods are cleaned, if necessary, before storage, with the hope that there will be no need for a further cleaning or finishing step before they are transported to a rig site. However, corrosion due to water and oxygen may quickly attack the precisely machined threads, which then cannot provide a satisfactory coupling without being cleaned again.
The exposed threaded ends of tubular metal goods are conventionally protected in one or more ways, so as to extend the period they can be stored. Closed-end thread protectors, usually plastic or elastomeric caps, or end caps made from metals such as steel, brass, or copper, are placed over the threaded ends thus providing protection from physical abuse, but this alone is not sufficient to do more than slow the corrosion process. Therefore, products such as API (American Petroleum Institute) modified thread compound, "Kendex Storage Compound" or similar fossil grease-based or wax compounds, have been applied to prevent or inhibit corrosion. These products can contain hazardous materials, such as lead, copper, zinc and hydrocarbons which typically are removed prior to downhole placement of the tubular goods. Various cleaning solutions, such as solvent varsol naphtha or diesel oil, are used in removing such materials. While in some cases the applied compounds and solids are captured and recycled, in many others they have been allowed to run or drip onto the ground below, presenting the problems of hazardous waste contamination and removal.
Various other corrosion prevention and inhibition compositions are known and in use, but they do not meet all of the requirements for the oil country installation. Some are toxic, and a number of them are carcinogenic. They are often difficult to apply, not sufficiently long lasting, and must often be cleaned if they are to be employed with a thread lubricant and sealant. In this respect, a thread sealant that has recently been widely adopted for use is "SEALLUBE", a product of the Loctite Corporation of Newington, Connecticut. This is an anaerobic composition of viscous nature that converts to a solid polymer in the absence of air. Compatibility of anticorrosion adjuvants with this composition is of particular importance because of its increasing use.
One corrosion inhibitor that has been employed for the protection of tubular goods and other steel products is sodium benzoate. It is usually combined with sodium nitrate for use as a corrosion inhibitor for ferrous metals and is easily applied because it dissolves in water. It does not afford, however, sufficiently long lasting protection, due to its high water solubility. Another class of materials that has been used comprises vapor phase inhibitors or vaporizable corrosion inhibitors (VCI), and these provide somewhat longer protection. This type of inhibitor sublimes into a vapor that condenses on the surface to be protected, and provides a film of 20 to 50 angstroms in thickness, that is replenished during the continuation of the sublimation action. The VCI compounds are sometimes disposed within a wrapping having a porous surface accessible to the metal, so that the vapors from the powder within the wrapping condense on the metallic surface and form a protective film. In some instances, the powders are contained within a bag or holder placed over the threaded end of the tubular goods. In either procedure, application and removal is overly time consuming, and cleaning of the tube stock may still be necessary, particularly where the powder remains in direct contact with the threaded surface. In addition, the protection afforded is less than desired.
Therefore, a continuing need exists for compositions effective to inhibit the corrosion of metallic tube goods, which are easy to apply, and which offer long-lasting protective effects. Moreover, with the use of such compositions, a thread protector which protects the precisely machined threads from physical abuse and which isolates or seals the treated threads and the corrosion inhibitor compositions from the environment is needed.